When you create a project, if you select the customer to fill out the project details, they will receive the invite in the email to do so.
If you fill out the project details, you can wait to invite the customer until the expert submits a proposal for their review. However, we recommend inviting them as soon as possible so they have visibility into the full process.
When you are ready to invite your customer you can add their email to the Stakeholders section of your project.